Customized illumination schemes for critical layers of 90nm node dense memory devices in ArF lithography: comparison between simulation and experimental results

Current 90nm Flash memory design introduces imaging critical points in several devices levels: active, poly, contacts, and first metallization. Among standard Resolution Enhancement Techniques (RET), Off axis illuminations play a fundamental role, because they are capable of providing better imaging contrast and improved process latitude in low K-1 regime with very dense structures. Starting from the simulation study of real device layer geometries, object of this work is to propose a solution in terms of illumination schemes and mask choice (binary or halftone) for each critical layer, considering K-1 around 0.35 in ArF lithography. Dedicated off axis illuminations will be compared to standard illumination modes, underlining the benefits in terms of ultimate resolution, process window and line edge roughness improvement. Experimental data confirmed the predicted gain in process robustness and, as expected, showed great line edge roughness improvement and less marginality to pattern collapse.